The present invention relates to a radiant wall burner apparatus suitable for use in a radiant-type furnace such an an ethylene decomposing furnace. More particularly, the present invention is concerned with a radiant burner apparatus capable of forming flames along surface wall surfaces so as to generate radiant heat which effectively heats an object such as, for example, a group of reaction tubes in an ethylene decomposing furnace.
FIG. 8 schematically shows a conventional radiant-type furnace, e.g., an ethylene decomposing furnace. The furnace has a group of reaction tubes 1 disposed in the center thereof, a main burner provided on the bottom of the furnace so as to heat the reaction tubes, and a multiplicity of radiant wall burners 4. In order to avoid various troubles which may be caused when the reaction tubes 1 are directly contacted by a flame, the radiant wall burners 4 are designed and arranged such that they form a flame along the surface of the furnace wall.
The construction of a typical known radiant wall burner is shown in FIG. 9. This burner 4 has a burner body 6 which extends through the center of the burner block 5 so as to project into the furnace. A gaseous fuel G is supplied to the burner body 6. Before entering the burner body 6, the gaseous fuel is mixed with primary air A.sub.1 supplied through a primary air inlet provided on the base end of the burner body 6. The fuel mixed with the primary air is radially sprayed through slits or multi-nozzle 8 which are formed on the outer peripheral surface of the burner body 6. An annular space defined between the inner peripheral surface of the burner block 5 and the outer peripheral surface 6 constitutes a passage 9 for secondary air A.sub.2 so that secondary air as additional combustion air is supplied into the furnace.
In operation, the primary air is aspirated by a the difference between the pressure of atmospheric air of the room temperature and the negative pressure which is created by the jet of the gaseous fuel G. The thus aspirated primary air is mixed in the gaseous fuel and the thus formed mixture is jetted from the slit nozzle 8 while inducing the secondary air so that the fuel is burnt to form a flame which spreads along the furnace wall surface 3.
In recent years, it has been attempted to use, as the combustion air for burning the fuel in this type of burner, heated excess air or combustion gas from a gas turbine for the purpose of saving energy. The use of such heated excess air or combustion gas in the radiant wall burner of the type described involves a risk that the gaseous fuel may be burnt explosively during mixing with the air. In order to obviate such a risk, it has been proposed to use burners designed to have independent passages for the gaseous fuel and the air down to the burner nozzle, as shown in FIGS. 10 and 11, so as to prevent pre-mixing of the fuel with air. More specifically, the burner shown in FIG. 10 has a triple-tube type burner body 10 constituted by a central tube defining a central passage 11 for a liquid fuel 0, an intermediate tube defining an inner annular passage for the gaseous fuel G, and an outer tube defining an outer annular passage 13 for the combustion air A. The nozzle is so designed as to cause the air-fuel mixture to suitably swirl so that a flame F is formed to spread along the wall surface 3.
On the other hand, the burner shown in FIG. 11 has a burner body 14 constituted by a fuel gas tube 15 and a combustion air pipe 16 surrounding the fuel gas tube 15. The downstream end of the gas tube 15 is branched into two tubes 15A, 15B which are suitably twisted to make the discharged fuel to swirl. In operation, the gaseous fuel G jetted from the burner nozzle swirls together with the air A and is burnt to form a flame F which spreads along the furnace wall surface 3.
The burners of the type shown in FIGS. 10 and 11 which are designed to prevent pre-mixing of the gaseous fuel with air are effective in preventing the explosive burning of the fuel, but involves a risk that the burning is retarded due to the use of the fuel having a high burning speed with the result that the flame is formed apart from the furnace wall surface so as to directly attack the reaction tubes 1. For instance, when a gaseous fuel having a high burning speed such as hydrogen gas is used as the fuel gas, there is a tendency that the burner forms a flame F.sub.a which rapidly grows towards the reaction tubes so as to directly attack the latter, with the result that the reaction tubes 1 are seriously damaged.